FR3077680A1 - TRANSMITTER, TRANSMITTER DEVICE AND DISPLAY SCREEN AND MANUFACTURING METHOD THEREOF - Google Patents

Abstract

The present invention relates to a transmitter (25) adapted to emit a first radiation, the transmitter (25) comprising: - a substrate (55), - a mesa consisting of a first semiconductor material having a first forbidden band value , the mesa having an upper side (70) and a lateral side (75), - a covering layer (45) comprising one or more radiation-emitting layers (85) constituted by a second semiconductor material having a second forbidden band value strictly less than the first forbidden band value, each radiation emitting layer (85) having a first portion (95) corresponding to the upper side (70) and a second portion (100) ) corresponding to the lateral side (75), a first thickness (e1) being defined for the first part (95) and a second thickness (e2) being defined for the second part (100), the second thickness (e2) being strictly lower at the first thickness (e1).

Description

* 54) TRANSMITTER, TRANSMITTER DEVICE AND DISPLAY SCREEN AND MANUFACTURING METHOD THEREOF.

FR 3,077,680 - A1 (57) The present invention relates to a transmitter (25) adapted to emit a first radiation, the transmitter (25) comprising:

- a substrate (55),

- a mesa made of a first semiconductor material having a first band gap value, the mesa having an upper side (70) and a lateral side (75),

- a covering layer (45) comprising one or more radiation emitting layer (s) (85) consisting of a second semiconductor material having a second band gap value strictly less than the first value band gap, each radiation emitting layer (85) having a first part (95) corresponding to the upper side (70) and a second part (100) corresponding to the lateral side (75), a first thickness (e1) being defined for the first part (95) and a second thickness (e2) being defined for the second part (100), the second thickness (e2) being strictly less than the first thickness (e1).

Transmitter, transmitter device and display screen and associated manufacturing method

The present invention relates to a transmitter. The present invention also relates to a transmitter device comprising at least two such transmitters. The present invention also relates to a display screen comprising a set of such transmitting devices. The present invention also relates to a method of manufacturing such a transmitter.

The luminescent structures comprise a stack of superimposed semiconductor layers structured so as to form a set of separate luminescent mesas. These structures are generally manufactured by eliminating by etching part of a stack of two-dimensional layers so as to define the luminescent mesas. The light emission is provided by a luminescent layer which is generally found at or near the top of the mesas.

Since the luminescent mesas are separated from each other, such structures allow easy control of the emission of each mesa, since each mesa can be independently supplied with electricity with a reduced risk of current leakage to a neighboring mesa. Due to the aforementioned advantages, it has been suggested to use such luminescent structures as part of display screens, each mesa forming a pixel if the screen is a monochrome screen or a sub-pixel if the screen is a full color screen. The spatial resolution of such a display screen is therefore directly related to the lateral dimensions of the mesa.

However, the exposed lateral sides of the mesas give rise to increased surface recombination of the carriers. The overall light emission efficiency (also called "wall outlet efficiency") of these structures therefore decreases with the lateral dimensions of the mesas, since reduced lateral dimensions lead to a relative increase in the surface of the lateral sides compared to on the surface of the luminescent layer. Consequently, the efficiency at the wall outlet of pixels or mesas-based display screens decreases when the resolution of the screen increases, in particular, when the lateral dimension of the mesas is of the order of 10 micrometers (pm). or less.

There is therefore a need for a light emitter having small lateral dimensions and having a high efficiency at the wall outlet.

To this end, the present description relates to a transmitter adapted to emit a first radiation, the transmitter comprising:

- a substrate,

a mesa, the mesa consisting of a first semiconductor material, the first semiconductor material having a first band gap value, the mesa having an upper side and a lateral side, the lateral side surrounding the upper side and extending between the substrate and the upper side,

a covering layer comprising one or more radiation emitting layer (s), at least one radiation emitting layer consisting of a second semiconductor material, the second semiconductor material having a second band value prohibited, the second prohibited band value being strictly less than the first prohibited band value, each radiation emitting layer having a first part corresponding to the upper side and a second part corresponding to the lateral side, a first thickness being defined for the first part and a second thickness being defined for the second part, the second thickness being strictly less than the first thickness.

According to specific embodiments, the transmitter comprises one or more of the following characteristics, taken separately or in any possible combination:

- at least one of the following properties is satisfied:

• the first part at least partially covers the upper side of the mesa and the second part at least partially covers the lateral side of the mesa;

• the second part forms at least one quantum well, and • the lateral side comprises a plurality of planar faces.

- at least one of the following properties is satisfied:

• the substrate consists of a semiconductor material, the mesa extending in a first direction perpendicular to the substrate from the substrate and being electrically connected to the substrate, the substrate having a main surface surrounding the mesa in a plane perpendicular to the first direction, the substrate further comprising an electrically insulating layer extending over the main surface, the insulating layer forming a barrier between the substrate and the covering layer, and • for each point on the lateral side, an axis corresponding to the direction crossing the point and perpendicular to the lateral side is defined, and in which the angle between a first direction perpendicular to the substrate and the axis is between 30 degrees and 80 degrees.

- at least one of the following properties is satisfied:

• at least one of the first semiconductor material and of the second semiconductor material is a nitride of elements III, and • a crystal structure is defined for the first semiconductor material, the crystal structure having at least one polar direction and at least a semi-polar direction, the upper side being perpendicular to the polar axis, an axis corresponding to the direction crossing the point and perpendicular to the lateral side being defined for each point on the lateral side, the axis being perpendicular to the semi-direction polar.

- at least one of the following properties is satisfied:

• the emitter further comprises a first electrical contact electrically connected to the first part, the emitter being configured to emit the first radiation when an electric current passes through the first electrical contact, the covering layer and the mesa, the first electrical contact being further electrically connected to the second part;

• the emitter further comprises a first electrical contact electrically connected to the first part, the emitter being configured to emit the first radiation when an electric current passes through the first electrical contact, the covering layer and the mesa, the first electrical contact comprising a first connection layer and a second barrier layer, the second barrier layer being interposed between the first connection layer and the covering layer, the first connection layer being made of a fourth material, the fourth material being an electrically conductive material or a semiconductor material, the second barrier layer consisting of an insulating material, the covering layer, the second barrier layer and the first connection layer forming a tunnel junction;

The covering layer comprises at least two superimposed radiation emitting layers made of the second semiconductor material, a first barrier layer made of a third semiconductor material being interposed between each pair of successive radiation emitting layers, the third material semiconductor having a third band gap value, the third band gap value being strictly greater than the second band gap value, and • the first radiation comprises a first set of electromagnetic waves, the radiation emitting layer being configured to emitting a second radiation comprising a second set of electromagnetic waves, the emitter further comprising a radiation converter configured to absorb the second radiation and to emit in response the first radiation, a wavelength being defined for each an electromagnetic wave, the first set corresponding to a first wavelength range and the second set corresponding to a second wavelength range, the first range having a first average wavelength and the second range having a second mean wavelength, the first mean wavelength being different from the second mean wavelength.

- at least one of the following properties is satisfied:

• the ratio between the first thickness and the second thickness is between 1.5 and 6;

• the mesa has a minimum lateral dimension and a height, the height being measured in a first direction perpendicular to the substrate and the minimum lateral dimension being measured in a plane perpendicular to the first direction, the height being strictly less than the minimum lateral dimension;

• the mesa forms a trunk having a base in contact with the substrate, the base being a rectangle;

• the mesa forms a trunk having a base in contact with the substrate, the base being a hexagon;

• the mesa has a height measured along a first direction perpendicular to the substrate, the height being between 100 nanometers and 1000 nanometers, and • the upper side has an area between 9 square micrometers and 900 square micrometers.

A transmitter device comprising at least two transmitters as defined above is also proposed.

According to specific embodiments, the transmitter device comprises one or more of the following characteristics, taken separately or in any possible combination:

- the lateral sides of the mesas are in contact with each other.

each transmitter comprises a first electrical contact electrically connected to the first part of the transmitter, the transmitter device further comprising a single connection structure, the connection structure comprising a mesa, a covering layer and a second electrical contact, the second electrical contact covering at least partially the upper side and at least partially the lateral side of the mesa of the connection structure, the second electrical contact being electrically connected to the substrate, each emitter being configured to emit the first corresponding radiation when a current electrical pass through the first corresponding electrical contact, the corresponding covering layer, the corresponding mesa, the substrate and the second electrical contact.

the transmitting device comprises three transmitters, each first radiation comprises a first set of electromagnetic waves, a wavelength being defined for each electromagnetic wave, each first set corresponding to a first range of wavelengths, each first range having a corresponding first average wavelength, the first average wavelength of each transmitter being different from the first average wavelength of each other transmitter.

A display screen comprising a set of transmitting devices as defined above is also provided.

This description also relates to a method of manufacturing a transmitter adapted to emit a first radiation, the method comprising the steps of:

- supply of a substrate,

- creation of a mesa made of a first semiconductor material, the first semiconductor material having a first band gap value, the mesa having an upper side and a lateral side, the lateral side surrounding the upper side and s 'extending between the substrate (55) and the upper side, and

- deposition on the mesa of a covering layer comprising one or more radiation emitting layer (s), at least one radiation emitting layer consisting of a second semiconductor material, the second semiconductor material having a second band gap value, the second band gap value being strictly less than the first band gap value, each radiation emitting layer having a first part corresponding to the upper side and a second part corresponding to the lateral side, a first thickness being defined for the first part and a second thickness being defined for the second part, the second thickness being strictly less than the first thickness.

This description further describes a method of manufacturing a transmitter device comprising a first transmitter and at least a second transmitter, each transmitter being adapted to emit a corresponding first radiation, the method comprising the steps of:

- supply of a substrate,

- Creation, for each transmitter, of a mesa made of a first semiconductor material, the first semiconductor material having a first band gap value, the mesa having an upper side and a lateral side, the surrounding lateral side the upper side and extending between the substrate and the upper side, and

- deposition on each mesa of a covering layer comprising one or more radiation emitting layer (s), at least one radiation emitting layer consisting of a second semiconductor material, the second semiconductor material having a second band gap value, the second band gap value being strictly less than the first band gap value, each radiation emitting layer having a first part corresponding to the upper side and a second part corresponding to the lateral side, a first thickness being defined for the first part and a second thickness being defined for the second part, the second thickness being strictly less than the first thickness.

According to a specific embodiment, the substrate has a first side and a second side, the first side supporting the mesas, the first side and the second side being parallel to each other, each first radiation comprising a first set of electromagnetic waves, the radiation emitting layer of each second emitter being configured to emit a second radiation comprising a second set of electromagnetic waves, the method further comprising a step of forming, for each emitter, a first connected electrical contact electrically to the first part, the emitter being configured to emit the first corresponding radiation when an electric current passes through the first electrical contact, the covering layer and the mesa. The method also includes a step of connecting each first electrical contact to a control circuit adapted to generate each electrical current and a step of placing, on the second side of the substrate, a radiation converter configured to absorb the second radiation and to emit in response the first radiation corresponding to the second emitter, a wavelength being defined for each electromagnetic wave, the first set of the second emitter corresponding to a first range of wavelengths and the second set corresponding to a second wavelength range, the first range having a first average wavelength and the second range having a second average wavelength, the first average wavelength being different from the second average wavelength.

Characteristics and advantages of the invention will appear clearly in the following description, provided only by way of nonlimiting example, and with reference to the appended drawings, in which:

FIG. 1 is a partial top view of a display screen comprising a set of transmitting devices,

FIG. 2 is a side view of a section of a transmitting device along the axis ll-ll in FIG. 1, each transmitting device comprising a set of transmitters,

- Figure 3 is an enlarged side view of a section of a transmitter of Figure 2,

FIGS. 4 to 12 are schematic views of the results at various stages of an example of a process for manufacturing a transmitting device,

- Figures 13 to 17 are schematic side views of examples of transmitting devices,

FIGS. 18 to 20 are schematic views of the results at various stages of another example of a process for manufacturing a transmitting device, and

- Figure 21 is a schematic side view of another example of a transmitting device.

A display screen 10 is partially shown in Figure 1 and shown schematically in Figure 12.

The display screen 10 is, for example, integrated into an electronic device such as a mobile phone, a tablet or a laptop. In another embodiment, the display screen 10 can be integrated into a dedicated display device such as a television set, a desktop computer screen, a smart watch or smart glasses.

The display screen 10 is configured to display a set of images.

The display screen 10 includes a set of transmitting devices 15 and a control circuit 20.

Each emitting device 15, also called "image element", or in short "pixel" is configured to emit at least one first radiation.

For simplification purposes, the emitting device 15 is called pixel 15 below.

For example, each pixel 15 is configured to emit one of a set of electromagnetic waves comprising three first radiations.

Alternatively, embodiments having a pixel configured to emit more or less than three radiations (for example, four) may be considered.

Each first radiation includes a first set of electromagnetic waves.

A wavelength is defined for each electromagnetic wave.

Each first set corresponds to a first range of wavelengths. The first wavelength range is the group formed by the set of wavelengths of the first set of electromagnetic waves.

A first average wavelength is defined for each first range of 10 wavelengths.

Each pixel 15 comprises at least one light emitter 25, and at least one connection structure 30. For example, each pixel 15 comprises three light emitters 25 and a single connection structure 30.

Each light emitter 25 is configured to emit a respective first radiation 15. In particular, each light emitter 25 is configured to emit the first respective radiation when a first electric current passes through the light emitter 25.

The first average wavelength of each light emitter 25 is, for example, different from the first average wavelength of each other light emitter 25 of the same pixel 15.

According to one embodiment, the first average wavelength of a light emitter 25 is between 430 nanometers (nm) and 480 nm, the first average wavelength of another light emitter 25 is between 500 nm and 560 nm and the first average wavelength of the third light emitter 25 is between 580 nm and 680 nm.

Embodiments in which the first average wavelengths of two different light emitters 25 of a single pixel 15 are identical can also be considered.

As shown in FIG. 2, each light emitter 25 comprises a substrate 30 55, a mesa 40, a covering layer 45, a first electrical contact 50, a radiation converter 52 and an insulating layer 60.

The substrate 55 is configured to support the mesa 40, the covering layer 45 and the first electrical contact 50.

The substrate 55 is, for example, common to all of the light emitters 25 and to the contact block or to the connection structure.

In certain embodiments, the substrate 55 can also comprise a support plate 120. In the embodiment shown in FIGS. 2 and 3, the substrate 55 does not include a support plate 120.

The substrate 55 is, for example, planar. A planar substrate is a substrate having a planar main surface 65.

A normal direction D is defined for the substrate 55. The main surface 65 of the substrate 55 is perpendicular to the normal direction D.

The main surface 65 surrounds each mesa 40 in a plane perpendicular to the normal direction D.

The substrate 55 consists of a first semiconductor material. A first band gap value is defined for the first semiconductor material.

The expression "band gap value" should be understood to mean the band gap value between the valence band and the material conduction band.

The band gap value is, for example, measured in electron volts (eV).

The valence band is defined as being, among the energy bands allowed for the electrons in the material, the band which has the highest energy while being completely filled at a temperature less than or equal to 20 Kelvin (K) .

A first energy level is defined for each valence band. The first energy level is the highest energy level in the Valencia band.

The conduction band is defined as being, among the energy bands allowed for the electrons in the material, the band which has the lowest energy while being completely filled at a temperature less than or equal to 20 K.

A second energy level is defined for each conduction band. The second energy level is the highest energy level in the conduction band.

Thus, each band gap value is measured between the first energy level and the second energy level of the material.

A semiconductor material is a material with a band gap value strictly greater than zero and less than or equal to 6.5 eV.

The first semiconductor material is, for example, an element III nitride. Element III nitrides are a group of materials including GaN, AIN and InN and alloys of GaN, AIN and InN.

According to one embodiment, the first material is GaN.

Doping is defined as the presence, in a material, of impurities leading to free charge carriers. Impurities are, for example, the atoms of an element that is not naturally present in the material.

When the impurities increase the volume density of the holes in the material, compared to the undoped material, the doping is of p type. For example, a GaN layer is doped p by adding magnesium (Mg) atoms.

When the impurities increase the density of the free electrons in the material, compared to the undoped material, the doping is of type n. For example, a GaN layer is doped n by adding silicon (Si) atoms.

The first material is for example n-doped. However, the type of doping may vary in certain embodiments.

The first material is, for example, a crystalline material. A crystal or crystalline material is a solid material whose constituents (such as atoms, molecules or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice which extends in all directions.

A crystalline structure is defined for the first material. In crystallography, the crystal structure is a description of the ordered arrangement of atoms, ions or molecules in a crystalline material.

The crystal structure is, for example, a polar structure. A polar structure is a crystal structure in which the barycenters of positive and negative electrical charges are separated in space.

The crystal structure has, for example, a polar direction, at least one non-polar direction and at least one semi-polar direction.

A polar direction is a direction along which the barycenters of positive and negative electrical charges are separated in space.

A non-polar direction is a direction along which the barycenters of positive and negative electrical charges are identical.

A semi-polar direction is a direction that forms a non-zero angle with both the polar axis and all non-polar directions of the material.

For example, the crystal structure is a hexagonal structure such as wurtzite. Wurtzite is the most common crystal structure of nitrides III. The polar axis of the wurtzite structure is called the c axis.

The normal direction D is, for example, parallel to the polar direction of the crystal structure.

The insulating layer 60 extends over the main surface 65. The insulating layer 60 surrounds, for example, each mesa 40 in a plane perpendicular to the normal direction D.

The insulating layer 60 is made of an electrically insulating material. For example, the insulating layer 60 is made of silicon oxide.

The insulating layer 60 forms a barrier between the covering layer 45 and the substrate 55. In particular, the insulating layer 60 prevents an electric current from passing between the covering layer 45 and the substrate 55 without passing through the mesa 40.

Each mesa 40 extends from the substrate 55 along the normal direction D.

Each mesa 40 has an upper side 70, a lateral side 75 and a base 80.

The mesa 40 is delimited along the normal direction D by the base 80 and the upper side 70.

Each mesa 40 is, for example, in the shape of a trunk.

In geometry, a trunk is the part of a solid that lies between one or two parallel planes cutting through the solid. An example of a trunk is a truncated pyramid.

For example, the mesa 40 is in the shape of a straight truncated pyramid. In geometry, a pyramid is a polyhedron formed by connecting a polygonal base 80 and a point, called the vertex. A right pyramid has its apex directly above the centroid of its base 80.

More specifically, the mesa 40 is in the shape of a truncated pyramid whose apex is aligned with the centroid of the base 80 along the normal direction D.

Each mesa 40 has a height h measured along the normal direction D and lateral dimensions measured in a plane perpendicular to the normal direction. Among the lateral dimensions, a minimum lateral dimension I of the mesa is defined as the dimension of the mesa 40, measured along the direction along which, among all the dimensions perpendicular to the normal direction D, the mesa 40 has the smallest dimension.

When the mesa 40 is in the shape of a truncated straight pyramid whose base 80 has an equal number of sides, the minimum lateral dimension I is the distance between two opposite sides of the base 80.

The height h is strictly less than the minimum lateral dimension I.

The height h is between 100 nm and 2 pm.

The mesa 40 is made of a semiconductor material. For example, the mesa 40 is made of the first semiconductor material.

The mesa 40 is electrically connected to the substrate 55. In one embodiment, the mesa 40 came integrally with the substrate 55.

The upper side 70 is, for example, planar. In the embodiment shown in Figure 2, the upper side 70 is perpendicular to the normal direction D.

The upper side 70 is polygonal.

As shown in Figure 1, the base 80 is, for example, rectangular. An upper side 70 square is an example of a rectangular upper side 70.

In other embodiments, the upper side 70 is hexagonal or triangular.

The upper side 70 has an area between 4 square micrometers (pm ² ) and 900 square micrometers (pm ² ).

The lateral side 75 extends between the substrate 55 and the upper side 70.

As shown in FIG. 3, the lateral side 75 surrounds the upper side 70. The lateral side 75 delimits the mesa 40 in a plane perpendicular to the normal direction D.

An axis A is defined for each point on the lateral side 75. The axis A corresponds to the direction crossing the point and perpendicular at this point to the lateral side 75.

An angle a between the normal direction and the axis A is, at any point on the lateral side 75, strictly less than 90 degrees (°). In particular, the angle a is between 30 and 80 °. For example, each axis A is perpendicular to a semi-polar direction.

In other words, an angle β between the normal direction D and a line on the lateral side 75, the line being included in a vertical plane comprising the normal direction D, is strictly greater than zero, for example, between 10 ° and 60 °.

According to one embodiment, each angle a is between 50 ° and 80 °. In other words, the angle β is between 10 ° and 40 °.

The lateral side 75 comprises, for example, a plurality of planar faces. In particular, when the mesa 40 is a truncated pyramid, each flat face is rectangular and extends from one side of the base 80 to one side of the upper side 70. In this case, the angles a of any two points of the same plane face are identical.

According to one embodiment, the lateral sides 75 of at least two transmitters 25 of a single pixel are in contact with each other.

The base 80 of the mesa 40 is in contact with the substrate 55.

The base 80 has a surface strictly greater than the surface of the upper side 70.

The base 80 is polygonal. A rectangular or hexagonal base 80 is an example of a polygonal base 80. For example, the shape of the base 80 is the same as the shape of the upper side 70.

According to the example shown in Figure 1, the sides of the bases 80 of each mesa 40 are parallel to each other.

The covering layer 45 is shown in more detail in FIG. 3.

The covering layer 45 covers at least part of the mesa 40.

The covering layer 45 is adapted to transmit the first electrical current from the mesa 40 to the first electrical contact 50.

The covering layer 45 extends over at least a part of the upper side 70 and at least a part of the lateral side 75. In particular, the covering layer 45 has a top part 77 in contact with the upper side 70 and a lateral part 78 in contact with lateral side 75.

Each covering layer 45 is interposed between the first electrical contact 50 and the mesa 40 so that the first electric current passing between the mesa 40 and the first electrical contact 50 passes through the covering layer 45.

The covering layer 45 comprises at least one radiation emitting layer 85. For example, the covering layer 45 comprises a plurality of superposed radiation emitting layers 85 and at least one first barrier layer 90.

The covering layer 45 is configured so that, when the first electric current passes through the covering layer 45, the first electric current passes through each radiation emitting layer 85.

Each radiation emitting layer 85 is configured to emit radiation when the first electric current passes through the radiation emitting layer 85. For example, each radiation emitting layer 85 is configured to emit second radiation.

Each second radiation includes a second set of electromagnetic waves.

Each second set of electromagnetic waves corresponds to a second range of wavelengths. The second wavelength range is the group formed by all the wavelengths of the second set of electromagnetic waves.

A second average wavelength is defined for each second wavelength range. The second average wavelength is different from the first average wavelength of the first radiation corresponding to the light emitter 25 of which the radiation emitting layer 85 forms a part. For example, the second average wavelength is strictly less than the first average wavelength.

According to another embodiment, the second average wavelength is equal to the first average wavelength of the first radiation.

The first semiconductor material is transparent to the second radiation.

Each radiation emitting layer 85 is made of a second semiconductor material.

The second semiconductor material has a second band gap value. The second band gap value is strictly less than the first band gap value.

The second semiconductor material is a crystalline material. For example, the second semiconductor material has the same crystal structure as the first semiconductor material. Embodiments in which the second semiconductor material has a structure different from the first semiconductor material can be envisaged.

The second semiconductor material is, for example, an III-N material. In particular, when the first semiconductor material is GaN, the second semiconductor material is InGaN.

Each radiation emitting layer 85 extends on the lateral side 75 and on the upper side 70.

In particular, each radiation emitting layer 85 covers at least part of the lateral side 75 and of the upper side 70. In other words, each radiation emitting layer 85 is supported by the lateral side 75 and the upper side 70.

Each radiation emitting layer 85 has a first part 95 and a second part 100.

The first part 95 of a radiation emitting layer 85 is the part of the radiation emitting layer 85 which is part of the top part 77 of the covering layer 45.

The first part 95 corresponds to the upper side 70. In particular, the first part 95 covers at least part of the upper side 70. For example, the first part 95 completely covers the upper side 70.

The first part 95 is perpendicular to the normal direction D.

The first part 95 has a first thickness e1. The first thickness e1 is measured along the normal direction D.

In the case of a single quantum well, the first thickness e1 is between 1 nm and 20 nm.

The first parts 95 of the set of radiation emitting layers 85 in the same emitter 25 are superimposed along the normal direction D. In other words, the first parts 95 form a stack of first parts 95 stacked along the normal direction D.

The second part 100 of a radiation emitting layer 85 is the part of the radiation emitting layer 85 which belongs to the lateral part 78 of the covering layer 45.

The second part 100 corresponds to the lateral side 75. In particular, the second part 100 covers at least part of the lateral side 75.

According to one embodiment, the second part covers at least 30 percent (%) of the surface of the lateral side 75. For example, the second part 100 covers at least 50% of the lateral side 75. Embodiments where the second part 100 covers at least 90% of the lateral side 75, in particular entirely covers the lateral side 75, can be envisaged.

The above values of the percentage of the surface of the lateral side 75 covered by the second part are, for example, calculated by considering only the surface of the lateral side 75 which is not in contact with the insulating layer 60.

However, embodiments where the percentage of the surface of the lateral side 75 covered by the second part is calculated by considering both the surface of the lateral side 75 which is not in contact with the insulating layer 60 and the surface of the lateral side 75 which is covered by the insulating layer 60 can be considered.

The second part 100 is perpendicular, at any point on the lateral side 75, to the axis A.

The second parts 100 of all the radiation emitting layers 85 in the same emitter 25 are superimposed on each other. In other words, these second parts 100 form a stack of second parts 100. The second parts 100 are stacked along the axis A.

Each second part 100 has a second thickness e2. The second thickness e2 is measured, at every point of the second part 100, along the corresponding axis A.

The second thickness e2 is strictly less than the first thickness e1. For example, a ratio of the first thickness e1 and the second thickness e2 is between 1.5 and 6.

The second part 100 is arranged so that a charge carrier energy level inside the second part 100 is strictly greater than a charge carrier energy level inside the first part 95.

The second thickness e2 is such that the second part 100 forms a quantum well for the charge carriers in the second material.

Structurally, a single quantum well is produced by intercalating a layer of a first semiconductor material between two layers of a second semiconductor material, the first semiconductor material and the second semiconductor material having different band gap values. In contrast, a multiple quantum well structure is a stack of semiconductor layers with alternating quantum wells and barriers.

Functionally, a quantum well is a structure in which a quantum confinement occurs, for at least one type of charge carriers, in one direction. The effects of quantum confinement occur when the dimension of the structure along this direction becomes comparable to or less than the de Broglie wavelength of the carriers, which are generally electrons and / or holes leading to energy levels. called "energy subbands".

In such a quantum well, carriers can only have discrete energy values, but are generally able to move within a plane perpendicular to the direction in which confinement occurs. The energy values available to carriers, also called "energy levels", increase as the dimensions of the quantum well decrease along the direction in which confinement occurs. Thus, since the second thickness e2 of the second part 95 is smaller than the first thickness e1 of the first part 100, the energy levels in the second part 95 are higher than the energy levels in the first part 100.

In quantum mechanics, the "de Broglie wavelength" is the wavelength of a particle when the particle is considered as a wave. The de Broglie wavelength of electrons is also called "electronic wavelength". The de Broglie wavelength of a charge carrier depends on the material in which the carrier is located.

A second part 100 having a second thickness e2 strictly less than the product of the electronic wavelength of the electrons in the second semiconductor material by five is an example of a quantum well.

The second thickness e2 is, for example, between 0.3 nm and 10 nm.

Each barrier layer 90 is made of a third semiconductor material. The third semiconductor material has a third band gap value. The third band gap value is strictly greater than the second band gap value.

In one embodiment, the third semiconductor material is the first semiconductor material. For example, the third semiconductor material is a nitride III material such as GaN.

The third semiconductor material is, for example, doped. The type of doping of the third semiconductor material is, for example, different from the type of doping of the first semiconductor material. In particular, the third semiconductor material is p-doped.

A barrier layer 90 is interposed between each pair of successive radiation emitting layers 85.

In one embodiment, a barrier layer 90 also covers the radiation emitting layer 85 which is farthest from the mesa 40. This barrier layer 90 forms a barrier between the radiation emitting layer 85 which is farthest from the mesa 40 and the outside of the transmitter 25.

Each barrier layer 90 has a thickness of between 1 nm and 30 nm. The first electrical contact 50 is configured to transmit the first electrical current from the control circuit 20 to the covering layer 45.

The first electrical contact 50 is in contact with the top part 77 of the covering layer 45. For example, the first electrical contact 50 is electrically connected both to the top part 77 and to the lateral part 78, and by Consequently, both at the first part 95 and at the second part 100 of the luminescent layer 85.

The first electrical contact 50 is, for example, made of a metallic material.

In another embodiment, the first electrical contact 50 comprises a connection layer and a second barrier layer.

The connection layer is made of a fourth material. The fourth material is an electrically conductive material or a semiconductor material. The fourth material is heavily doped with a first type of conductivity with dopants at a dopant concentration greater than 10 ¹⁹ atoms / cm ³ , preferably greater than 10 ² atoms / cm ³ .

The second barrier layer is made of an electrically insulating material.

The second barrier layer is interposed between the connection layer and the covering layer 45.

The second barrier layer is configured such that the covering layer 45, the second barrier layer and the connecting layer form a tunnel junction.

In such a context, the covering layer is a heavily doped semiconductor of a second type of conductivity with dopants at a dopant concentration greater than 10 ¹⁹ atoms / cm ³ , preferably greater than 10 ²⁰ atoms / cm ³ . The second type of conductivity is different from the first type of semiconductor.

A tunnel junction is a structure comprising a barrier, such as an insulating layer or a thin electrical potential, between two electrically conductive materials. Due to the thinness of the barrier, electrons can pass through the barrier by the quantum tunneling technique even if the barrier is made of an insulating material.

The second barrier layer has a thickness of between 50 nm and 300 nm.

The radiation converter 52 is adapted to convert the second radiation to the first radiation.

The radiation converter 52 is a photoluminescent material, for example, a phosphorus or a nanophosphorus.

As a variant, the photoluminescent material is a set of particles. An example of a photoluminescent material is a yttrium-aluminum garnet (YAG Yttrium-Aluminum Garnet) activated by the trivalent cerium ion, also called YAG: Ce or YAG: Ce3 +. The average particle size of conventional photoluminescent materials is greater than 5 µm.

In one embodiment, the photoluminescent material is a matrix having monocrystalline particles in the nanometric range of a semiconductor material, also hereinafter called semiconductor nanocrystals or nanophosphorus particles, dispersed therein.

According to one embodiment, the average size of the nanocrystals is in the range from 0.5 nm to 1,000 nm, preferably from 0.5 nm to 500 nm, more preferably from 1 nm to 100 nm, in particular from 2 nm to 30 nm. For dimensions less than 50 nm, the photoconversion properties of semiconductor nanocrystals essentially depend on quantum confinement phenomena. Semiconductor nanocrystals therefore correspond to quantum dots or quantum dots.

According to one embodiment, the semiconductor material of the semiconductor crystals is selected from the group comprising cadmium selenide (CdSe), indium phosphide (InP), cadmium sulfide (CdS), zinc sulfide (ZnS), selenide zinc (ZnSe), cadmium telluride (CdTe), zinc telluride (ZnTe), cadmium oxide (CdO), zinc and cadmium oxide (ZnCdO), cadmium and zinc sulfide (CdZnS), cadmium selenide and zinc (CdZnSe), silver and indium sulfide (AglnS2), and a mixture of at least two of these compounds.

The matrix is made of an at least partially transparent material. The matrix is for example made up of silica. The matrix is for example made up of at least one partially transparent polymer, in particular of silicon, epoxy or polyacetic acid (PLA). The matrix may consist of at least one partially transparent polymer used with three-dimensional printers, such as PLA. According to one embodiment, the matrix contains from 2% to 90%, preferably from 10% to 60%, by mass of nanocrystals, for example, approximately 20% by mass of nanocrystals.

According to other possible embodiments, the radiation converter 52 comprises a group of semiconductor particles housed in a photosensitive resin. As shown in FIG. 2, the radiation converter 52 is supported by a lower face 102 of the substrate 55 opposite the main surface 65, and facing the mesa 40.

The lower face 102 is, for example, parallel to the main surface 65. In the example shown in FIG. 2, the lower face 102 delimits the substrate 55 along the normal direction D.

The substrate 55 is, for example, delimited along the normal direction D by the main surface 65 and the lower surface 102.

A distance between the lower surface 102 and the main surface 65, measured along the normal direction is, for example, between 500 nm and 50 µm.

The connection structure 30 is configured to electrically connect the substrate 55 and the control circuit 20.

The connection structure 30 comprises, for example, a mesa 40, a covering layer 45 and a second electrical contact 105.

The mesa 40 and the covering layer 45 of the connection structure 30 are identical to the mesa 40 and the covering layer 45 of the light emitters.

The second electrical contact 105 electrically connects the control circuit 20 and the substrate 55. For example, the second electrical contact 105 connects the control circuit 20 and the substrate 55 through the insulating layer 6Q.

The second electrical contact 105 consists of an electrically conductive material such as a metallic material.

The second electrical contact 105 is supported by the mesa 40 and the covering layer 45 of the connection structure 30. For example, the second electrical contact 105 covers at least part of the top part 77 and of the side part 78 of the connection structure 30.

The control circuit 20 is configured to generate the first electric current corresponding to each light emitter 25 and to transmit each first electric current to the corresponding light emitter 25.

The control circuit 20 comprises, for example, connection pads 110 each connected to a first or second electrical contact 50, 105.

More specifically, the corresponding connection pad 110 ^- to the second electrical contact 105 is in contact with a part of the second electrical contact 105. Said portion of the second electrical contact 105 is interposed between the first portion 95 of the corresponding covering layer 45 and the connection pad 110.

The operation of the light emitter 25 will now be described.

When the control circuit 20 generates the first electric current, the first electric current passes, successively, through the second electric contact 105, the substrate 55, the mesa 40, the covering layer 45 and the first electric contact 50.

The current flow leads to the arrival of electrons and holes in each luminescent layer 85. The recombination of electron-hole pairs in the luminescent layer or layers 85 leads to the emission of the second radiation.

At least part of the second radiation is absorbed by the converter 52. The absorption of the second radiation causes the converter to emit the first radiation.

During the operation of the light emitter 25, the charge carriers are repelled by the second parts 100 of the luminescent layer (s) 85 because the energy levels of the charge carriers in the second parts 100 are more higher than the load levels of the same carriers inside the first parts 95. The load carriers are therefore separated from the lateral side 75 of the mesa 40.

The surface recombination of the carriers on the lateral side 75 of the mesa 40 is therefore reduced when compared to a light emitter 25 which does not include second parts 100. Consequently, the emission efficiency of the light emitter 25 is higher than that of a light emitter 25 known in the prior art.

Such an effect increases when the lateral dimension of the mesas 40 decreases. In addition, this effect is stronger if 30% or more of the area of the lateral side 75 is covered by the second part 100.

The use of a second part 100 thinner than the first part 95 is a way of obtaining higher energy levels in the second part 100 than in the first part 95 which is easily reproducible when the second part 100 is thin enough to form a quantum well. A first thickness to second thickness ratio of between 1.5 and 6 corresponds to an energy difference between the first and second parts 95, 100 which allows good repulsion of the carriers from the second part 100.

The deposition of the luminescent layers 85 on a mesa 40 whose angle a is between 10 ° and 50 ° makes it possible to easily obtain such a thinner second part 100. Indeed, the material deposited on such lateral faces 75 grows more slowly than when it is deposited on the upper side 70 due to the geometry of the conventional material deposition chambers.

Such easy obtaining of pixel 15 is now described with reference to an example of implementation of a method for manufacturing such a pixel 15 which is illustrated diagrammatically in FIGS. 4 to 12.

A method of manufacturing the pixel 15 includes a supply step, a creation step, an isolation step, a deposition step, a training step, a connection step and a placement step.

During the supply step, the substrate 55 is supplied. During the supply step, the substrate 55 comprises a support plate 120 supporting the substrate 55. The support plate 120 is, for example, a silicon or sapphire plate (see in particular FIG. 4).

During the creation step, each mesa 40 is created. For example, each mesa 40 is created by elimination by etching of part of the substrate 55 (see in particular FIG. 5).

During the isolation step, the insulating layer 60 is deposited on selected areas of the main surface of the substrate 55.

For example, the electro-insulating material is deposited on the substrate 55 and the mesas 40, and then removed from the mesas 40. In other embodiments, a layer of photosensitive resin is deposited on the mesas 40 so that the material electrical insulator is only deposited on the main surface 65.

The deposition step comprises the deposition of each covering layer 45 on the corresponding mesa 40 (see in particular FIG. 6). For example, an identical covering layer 45 is deposited on each mesa 40.

The deposition is, for example, carried out using a deposition technique such as chemical vapor deposition by organometallic compounds (Metal-Organic Chemical Vapor Deposition - MOCVD).

MOCVD is also called "MOVPE", which stands for "Metal-Organic Vapor Phase Epitaxy" (vapor phase epitaxy with organometallic compounds). Other chemical vapor deposition (CVD) processes can also be considered.

However, other deposition techniques can be used, such as molecular beam epitaxy (Molecular Beam Epitaxy - MBE), gas source MBE (GSMBE), organometallic MBE (MOMBE), plasma-assisted MBE (PAMBE), atomic layer epitaxy (Atomic-layer Epitaxy - ALE) or hydride vapor epitaxy (Hydride Vapor Phase Epitaxy - HVPE).

Due to the different crystal orientations of the upper side 70 and the lateral side 75, the deposition of the luminescent layers 85 results in a second thickness e2 less than the first thickness e1.

During the training step, each first electrical contact 50 is formed. For example, each first electrical contact 50 and each second electrical contact 105 are deposited simultaneously on the corresponding mesas 40 and the covering layers 45 as illustrated in FIG. 7.

In one embodiment, a protective resin layer is formed, before deposition, on the substrate 55, the mesas 40 and the covering layers 45 and shaped to leave only visible the areas on which the electrical contacts 50, 105 must be deposited (see figures 8 and 9).

The electrical contacts 50, 105 are, for example, deposited using a metal deposition technique such as electron beam deposition, thermal evaporation and cathodic deposition.

Each first and second electrical contact 50, 105 is then electrically connected to the control circuit 20 during the connection step (see FIG. 9).

The support plate is removed from the substrate 55 to expose the underside 102 of the substrate 55 (see Figure 10).

Each radiation converter 52 is then formed opposite the corresponding mesa 40 on the underside 102. Lithography is an example of a suitable method for setting up such a converter (see FIG. 11).

The fabrication of a pixel has been previously described in the case of a pixel 15 comprising several light emitters. A method of manufacturing a single light emitter 25 may, however, include the supplying step and the depositing step, provided that only a mesa 40 is created during the creation step and that the covering layer 45 is deposited only on the mesa 40 created during the deposition step.

Each manufacturing process is thus easy to implement.

The transmitter 25 also offers advantages which are now described.

When the first electrical contact 50 is electrically connected to the second part 100, the electric current propagates between the second part 100 and the first electrical contact 50 along the axis A. When the axis A is parallel to a semipolar direction of the crystal structure, the injection of holes in the covering layer 45 is facilitated.

Due to the larger contact surface between the covering layer 45 and the first electrical contact 50, the voltage is reduced and the efficiency at the wall outlet is improved (see FIG. 14).

The presence of the insulating layer 60 reduces the electrical losses by means of a short circuit between the substrate 55 and the covering layer 45. The same effect is obtained if the mesas 40 of neighboring light emitters are in contact. with each other, since in this case the electrical contact between the covering layers 45 and the substrate 55 is eliminated.

When the crystal structure of the material is hexagonal, a hexagonal shape of the base 80 allows the properties of the sides 75 to be identical with each other due to the hexagonal symmetry of the wurtzite.

In addition, the hexagonal or rectangular bases 80 allow the mesas 40 to be arranged on the substrate 55 in a compact manner, and therefore the pixel 15 to be smaller. The resolution of a display screen 10 including a set of pixels 15 is therefore higher.

The use of light converters 52 allows light emitters 25 having identical luminescent layers 85 to emit different first rays, in particular different colors of first rays, while being easily manufactured, since only one deposition step is performed to deposit all of the luminescent layers 85.

When each of the three light emitters 25 of a single pixel 15 emits a different first radiation, the pixel can be used as a color pixel on a display screen.

However, embodiments in which one or more of the light emitters 25 do not include a radiation converter 52 can be envisaged. In this case, the radiation emitted by the luminescent layers 85 is the first emission.

For example, two of the light emitters 25 include radiation converters 52 but the third light emitter 25 does not include a radiation converter 52, in particular when the third light emitter emits first blue radiation. In another embodiment, none of the light emitters 25 comprises a radiation converter 52, the luminescent layers 85 of the light emitters 25 being configured to emit first rays having different average wavelengths, for example if the second 25 light emitter materials are different.

The light emitters 25 lacking a radiation converter 52 are more efficient.

In addition, embodiments in which each light emitter 25 comprises a radiation converter 52 can be envisaged. For example, each radiation emitting layer 85 is ultraviolet radiation, and each radiation converter 52 converts ultraviolet radiation to the first corresponding radiation.

Mesa 40 has been described above in the case of a truncated pyramid shape. However, the shape of the mesa 40 may vary.

In one embodiment, the mesa 40 is in the shape of a truncated cone. For example, the upper side 70 and the base 80 are circular.

In the example above, only the second part 95 has been described as a quantum well. However, embodiments in which the first part 95 forms a quantum well can be envisaged. The emission efficiency of quantum wells is often higher than that of thicker layers.

Note that a planarization layer can be used. A planarization layer is a layer of material deposited on the substrate 55, on the mesas 40 and on the covering layers 45 so that the mesas 40 and the covering layers 45 are incorporated in the planarization layer which forms a flat surface. . A flat surface can be advantageous for the treatment of the device and can allow a more uniform electrical injection (see figure 17).

The planarization layer is, for example, made of the first semiconductor material.

In one embodiment, the planarization layer is doped. In particular, the planarization layer has a different type of doping than that of the mesa 40.

In a specific example, the planarization layer consists of p-doped GaN.

The luminescent layer 85 has been described as a compact layer of a single material. Embodiments in which the luminescent layer 85 is a superlattice are also envisaged. Superlattices are layers formed by a stack of sublayers of two or more different materials, forming a pattern that is repeated along the stacking direction, the sublayers being so thin that a quantum coupling between sublayers exist.

The various semiconductor materials described above are nitride III materials with a wurtzite structure. However, other crystal structures and materials can be used.

For example, any of the first, second, third and fourth semiconductor material can be chosen from arsenide materials such as AlAs, GaAs, InAs, from phosphide materials such as AIP, GaP, InP, from ll-VI materials such as ZnSe, CdSe, ZnTe, CdTe, among IV materials such as Si and Ge, or among any alloy of these materials.

As a general illustration of the various embodiments which can be considered, reference is made in particular to FIGS. 13 to 17 which are schematic side views of examples of pixels.

Figure 13 corresponds to a microLED mesa; Figure 14 to an overlapping metal p; FIG. 15 with tunnel-effect junction contact; Figure 16 to a compact mesa microLED and Figure 17 to a compact mesa microLED with planarized surface.

In addition, embodiments in which superlattices are added below the quantum wells can be considered.

Another example of a pixel 15 manufacturing process is illustrated in FIGS. 18 to 20.

According to this example, the covering layer 45 is deposited before depositing the insulating layer 60. The covering layer 45 thus covers both the mesas 40 and the main surface 65 (see FIG. 18).

During a following removal step, the part of the covering layer 45 which covers the main surface 65 is removed, for example by etching (see FIG. 19). In one embodiment, the part of the covering layer 45 which covers the lowest part of the mesas 40, and which is thus in electrical contact with the main surface 65, is also removed.

The isolation step can optionally be carried out after removal to cover the main surface 65 with an electrically insulating material (see FIG. 20).

The connection structure 30 has been described above as comprising a mesa 40, a covering layer 45 and a second electrical contact 105. However, simpler embodiments in which the connection structure comprises only the second electrical contact 105 can be considered. In this case, the second electrical contact is, for example, a block of electrically conductive material whose total height is equal to the total height of the emitters 25 (see FIG. 21).

Claims (10)

1Emitter (25) adapted to emit a first radiation, the emitter (25) comprising: - a substrate (55), - a mesa (40), the mesa (40) consisting of a first semiconductor material, the first semiconductor material having a first band gap value, the mesa (40) having an upper side (70) and a side lateral (75), the lateral side (75) surrounding the upper side (70) and extending between the substrate (55) and the upper side (70), - a covering layer (45) comprising one or more radiation emitting layer (s) (85), at least one radiation emitting layer (85) consisting of a second semiconductor material, the second material semiconductor having a second band gap value, the second band gap value being strictly less than the first band gap value, each radiation emitting layer (85) having a first portion (95) corresponding to the upper side (70) and a second part (100) corresponding to the lateral side (75), a first thickness (e1) being defined for the first part (95) and a second thickness (e2) being defined for the second part (100), the second thickness (e2 ) being strictly less than the first thickness (e1). 2, - Transmitter according to claim 1, in which at least one of the following properties is satisfied: - The first part (95) at least partially covers the upper side (70) of the mesa and the second part (100) at least partially covers the lateral side (75) of the mesa (40); the second part (100) forms at least one quantum well, and - the lateral side (75) comprises a plurality of planar faces. 3. - Transmitter according to claim 1 or 2, in which at least one of the following properties is satisfied: - the substrate (55) consists of a semiconductor material, the mesa (40) extending along a first direction (D) perpendicular to the substrate (55) from the substrate (55) and being connected electrically to the substrate (55), the substrate (55) having a main surface (65) surrounding the mesa (40) in a plane perpendicular to the first direction (D), the substrate (55) further comprising an electrically insulating layer ( 60) extending over the main surface (65), the insulating layer (60) forming a barrier between the substrate (55) and the covering layer (45), and - for each point on the lateral side (75), an axis (A) corresponding to the direction crossing the point and perpendicular to the lateral side (75) is defined, and in which the angle (a) between a first direction (D) perpendicular to the substrate (55) and the axis (A) is between 30 degrees and 80 degrees. 4. - Transmitter according to any one of claims 1 to 3, in which at least one of the following properties is satisfied: at least one of the first semiconductor material and the second semiconductor material is a III nitride material, and - A crystal structure is defined for the first semiconductor material, the crystal structure having at least one polar direction and at least one semi-polar direction, the upper side (70) being perpendicular to the polar axis, an axis corresponding to the direction crossing the point and perpendicular to the lateral side (75) being defined for each point on the lateral side (75), the axis (A) being perpendicular to the semi-polar direction. 5. - Transmitter according to any one of claims 1 to 4, in which at least one of the following properties is satisfied: - the emitter (25) further comprises a first electrical contact (50) electrically connected to the first part (95), the emitter (25) being configured to emit the first radiation when an electric current passes through the first electrical contact (50), the cover layer (45) and the mesa (40), the first electrical contact (50) being further electrically connected to the second part (100); - the emitter (25) further comprises a first electrical contact (50) electrically connected to the first part (95), the emitter (25) being configured to emit the first radiation when an electric current passes through the first electrical contact (50), the cover layer (45) and the mesa (40), the first electrical contact (50) comprising a first connection layer and a second barrier layer, the second barrier layer being interposed between the first connection layer and cover layer (45), the first connection layer being made of a fourth material, the fourth material being an electrically conductive material or a semiconductor material, the second barrier layer being made of an insulating material, the cover layer (45), the second barrier layer and the first connection layer forming a tunnel junction; the covering layer (45) comprises at least two superimposed radiation emitting layers (85) made of the second semiconductor material, a first barrier layer (90) made of a third semiconductor material being interposed between each pair of layers successive radiation emitters (85), the third semiconductor material having a third band gap value, the third band gap value being strictly greater than the second band gap value, and - the first radiation comprises a first set of electromagnetic waves, the radiation emitting layer (85) being configured to emit a second radiation comprising a second set of electromagnetic waves, the emitter (25) further comprising a radiation converter (52) configured to absorb the second radiation and to emit in response to the first radiation, a defined wavelength for each electromagnetic wave, the first set corresponding to a first range of wavelengths and the second set corresponding to a second wavelength range, the first range having a first average wavelength and the second range having a second average wavelength, the first average wavelength being different from the second average wavelength. 6.- Transmitter according to any one of claims 1 to 5, in which at least one of the following properties is satisfied: the ratio between the first thickness (e1) and the second thickness (e2) is between 1.5 and 6; - the mesa (40) has a minimum lateral dimension (I) and a height (h), the height (h) being measured in a first direction (D) perpendicular to the substrate (55) and the minimum lateral dimension (I) being measured in a plane perpendicular to the first direction (D), the height (h) being strictly less than the minimum lateral dimension (I); - the mesa (40) forms a trunk having a base (80) in contact with the substrate (55), the base (80) being a rectangle or a hexagon; - the mesa (40) has a height (h) measured along a first direction (D) perpendicular to the substrate (55), the height (h) being between 100 nanometers and 1000 nanometers, and - The upper side (70) has an area between 9 square micrometers and 900 square micrometers. 7, - Transmitter device comprising at least two transmitters (25) according to any one of claims 1 to 6. 8, - Display screen comprising a set of transmitting devices (15) according to claim 7. 9, - Method for manufacturing a transmitter (25) adapted to emit a first radiation, the method comprising the steps of: - supply of a substrate (55), - Creation of a mesa (40) made of a first semiconductor material, the first semiconductor material having a first band gap value, the mesa (40) having an upper side (70) and a lateral side ( 75), the lateral side (75) surrounding the upper side (70) and extending between the substrate (55) and the upper side (70), and - depositing on the mesa (40) a covering layer (45) comprising one or more radiation emitting layer (s) (85), at least one radiation emitting layer (85) consisting of a second semiconductor material, the second semiconductor material having a second band gap value, the second band gap value being strictly less than the first band gap value, each radiation emitting layer (85) having a first portion ( 95) corresponding to the upper side (70) and a second part (100) corresponding to the lateral side (75), a first thickness (e1) being defined for the first part (95) and a second thickness (e2) being defined for the second part (100), the second thickness (e2) being strictly less than the first thickness (e1). 10, -Process for manufacturing a transmitting device (15) comprising a first transmitter (25) and at least a second transmitter (25), each transmitter (25) being adapted to emit a corresponding first radiation, the method comprising the steps from: - supply of a substrate (55), - Creation, for each transmitter (25), of a mesa (40) consisting of a first semiconductor material, the first semiconductor material having a first band gap value, the mesa (40) having a top side (70) and a lateral side (75), the lateral side (75) surrounding the upper side (70) and extending between the substrate (40) and the upper side (70), and - depositing on each mesa (40) a covering layer (45) comprising one or more radiation emitting layer (s) (85), at least one radiation emitting layer 5 (85) consisting of a second semiconductor material, the second semiconductor material having a second band gap value, the second band gap value being strictly less than the first band gap value, each radiation emitting layer (85) having a first portion (95) corresponding to the upper side (70) and a second part (100) corresponding to the lateral side (75), a first thickness (e1) being defined for the first part (95) and a second thickness (e2) being defined for the second part (100), the second thickness e2) being strictly less than the first thickness (e1).